Porous membrane adsorbers comprise membranes which carry functional groups, ligands or reactants on their inner and outer surfaces, and which are capable of interaction with at least one substance in a liquid phase which is in contact with the membrane. See, generally, PCT application Ser. No. 92/00805. Transport of the liquid phase through the membrane is induced by a pressure differential across the membrane. The term "membrane adsorber" is to be understood as a generic name for various kinds of membrane adsorbers such as membrane ion exchangers, ligand membranes, and activated membranes, each of which may be subclassified in accordance with specific types of functional groups, ligands, and reactants.
The separation of substances from a liquid phase by means of membrane adsorbers is conventionally carried out by directing the liquid phase bearing the substance to be separated to a feed inlet chamber of a filtration unit, and, by virtue of the pressure difference between the feed inlet and the membrane's permeate outlet, the liquid passes through the pores of the membrane adsorber layers. To heighten adsorption capacity, several sequential membrane adsorber layers are often employed, which are interposed between the feed inlet and the permeate outlet in such a manner that the liquid phase must sequentially pass through all the membrane adsorber layers. Corresponding to their specific adsorption, the individual substances to be separated become affixed to the inner or outer surfaces of the membrane adsorber layers, while the permeate freed from the removed substances is conducted out of the permeate chamber. The adsorbed substances on the membrane surfaces are then selectively desorbed and elutriated by suitable elutriation means.
Filtration units with several layers of porous membranes adsorbers arranged in the form of a membrane stack are known. See German Patent Nos. DE A1 38 04 430 and DE A1 44 32 628. However, their design calls for sealing the periphery of membrane adsorbers in the stack, which is expensive. Such edge sealing must be carefully done so that the liquid phase will be forced to pass through the membrane layers sequentially from the first feed side of the first layer through all the layers to the final permeate side surface of the last membrane layer. The edge sealings comprise either sealing compounds applied to the outer periphery of the membrane stacks or closure rings, i.e., plates which seal off the peripheral zones of the membrane stacks from the housing of the filtration unit, all to prevent any by-passing of the membrane adsorber layers. A further disadvantage of such a design is that the sealing of the membrane adsorber layers must be done by the manufacturer of the filtration unit, effectively preventing customization of the units and adsorber elements so as to be adaptable to the particular separation the task at hand.
There is therefore a need in the art for a membrane adsorber filtration unit wherein no edge sealing is required, and which is readily adaptable to fit a desired separation, and which may be scaled up into production scale operations.